1. Field of the Invention
The present invention relates to a digital television (TV) broadcast signal receiver that can receive digital television broadcast signals such as ATSC (Advanced television systems Committee).
2. Description of the Related Art
In the North American Continent where an ATSC digital television broadcast (it is abbreviated to a hereinafter digital TV broadcast) is performed, plains are dotted with metropolises, so that various digital TV broadcast signals broadcasted in the suburbs of each metropolis can be received at other cities or the halfway point of the cities. In consideration from a user who receives the TV broadcast signals, since many TV broadcast signals are transmitted in various directions, it is necessary to regulate a direction of an antenna in an orientation to a TV broadcasting station from which a program which he wants to watch is delivered. Therefore, a multi-directional antenna such as a smart antenna is put into practical use.
As described in Japanese Laid-Open Patent Publication No. 10-233969, the TV broadcast signal receiver is generally set preferentially to receive a channel with a higher sensitivity of a TV broadcast signal. In Japanese Laid-open Patent Publication No. 2002-335458, a digital TV broadcast signal receiver displays numbers of receivable channels in different colors corresponding to sensitivities of TV broadcast signals, for visually indicating signal receiving conditions to the user. In Japanese Laid-Open Patent Publication No. 2002-353832, field strength of received TV broadcast signals and error rates of digital data are used to set a receive direction of an antenna in a digital TV broadcast receiver. In Japanese Laid-Open Patent Publication No. 2000-269786, which relates to FM broadcasting, in an area having many broadcast stations channels with low noise broadcast signals are selected, and in another area having a few broadcast stations, the conditions for noise of the broadcast signals is sweetened in order to increase a number of channels selectable.
According to the EIA-909 technical standard, it is provided that a smart antenna has sixteen signal receiving directions in respective directions where a circle is divided into sixteen. A digital TV broadcast signal receiver in compliance with the EIA-909 technical standard can adjust the signal receiving direction of the multi-directional antenna such as the smart antenna in all sixteen signal receiving directions.
By the way, there are many types of the multi-directional antenna, for example, a type for rotating an antenna with a motor for switching the signal receiving direction, or a type with a plurality of antennas and electronic switches in which a signal receiving direction is switched by switching on and off of the electronic switches. A term necessary for switching the signal receiving direction of the multi-directional antenna due to switching on and off of the electronic switches is approximately 10 ms extent with no relation in model. In contrast, a term necessary for switching the signal receiving direction of the multi-directional antenna in which the antenna is rotated with the motor is uneven in a range from 100 ms to 200 ms extent due to power of the motor and angle of rotation of the antenna. When the digital TV broadcast signal receiver has no function for distinguishing the kinds of the connected multi-directional antennas or for setting a term for switching the signal receiving direction optionally, the term for switching the signal receiving direction of the digital TV broadcast signal receiver is set to the longest term necessary for switching the signal receiving direction of the multi-directional antenna among the ones available in the market.
In general, a direction having the highest sensitivity of the TV broadcast signal among the directions in which the TV broadcast signal can be received is defined as an optimum signal receiving direction with respect to each channel. Then, the switching operation of the TV broadcast signal receiver is performed whenever a user chooses a channel so that the signal receiving direction of the multi-directional antenna is switched to the optimum signal receiving direction of the channel which is selected by the user. While a term for switching the signal receiving direction of the digital TV broadcast signal receiver, no image is displayed on a monitor screen, and the switching of the channel will be delayed. Especially when the user reshuffles the channel frequently, the switching operation of the signal receiving direction of the multi-directional antenna cannot catch up with the channel reshuffling operation, and it causes the irritation of the user.